//
// Created by nicemoe on 2021/9/5.
//

#include  <iostream>
#include <cstdlib>

using namespace std;


double hmean(double a, double b);

int main() {

    double x, y, z;
    cout << "Enter two numbers: ";
    while (cin >> x >> y) {
        z = hmean(x, y);
        cout << "Harmonice mean of " << x << " and " << y << " is " << z << endl;
        cout << "Rnter next set of numbers <q to quit>:";
    }
    cout << "Bye!\n";
    return 0;
}

double hmean(double a, double b) {
    if (a == -b) {
        cout << "untenable argument to hmean()\n";
        abort();
    }
    return 2.0 * a * b / (a + b);
}